Hmm, so this and bug 623452 and bug 623456 are all one thing, and that thing is that on whatever code path these WinXP slaves hit, opacity gives a different color depending on whether you set it before the first time it's drawn, or cause it to be redrawn? The other two set opacity on something already drawn, this one resizes a box with an opacity: 0.5 border.

Is there anything that any of the logs would have that would tell us more about the actual state?
The Win2K3 logs say the same thing in the json sandbox spew at the start, "layersGPUAccelerated":false, but they pass all the random-if tests, which certainly makes it look like it was false for them, is set to false for XP but that is an error and it isn't actually, and that just anyAccel vs none isn't a sharp enough razor to divide passing from random.

Because at the time, I didn't realize that the problem was that we knew that we would get crap results on tests like these when we were using hardware acceleration, but we didn't know that we were using it on these slaves, so I thought maybe the failures meant that... dunno, we drew like crap on Win XP, which we hadn't ever tested before.

Created attachment 503164[details][diff][review]
[checked in] temporarily annotate them
This feels a little like cheating, but it will free up I don't know how many build slaves to go back to building on Windows, instead of running 12 test jobs every push, 11 of which are currently hidden.

Comment 20 through comment 22 are not this bug -- they're a different (new) MacOS-specific issue, for which I've filed Bug 627560. (This bug is WinXP specific)
Adding a few notes to bug summary, so this stops being the target of mis-starring.